The instant invention generally relates to asynchronous transfer mode (ATM) networks and more particularly to ATM networks incorporating remotely located ATM nodes.
An ATM network is a connection-oriented communications network incorporating packet-switching, wherein messages are segmented and incorporated into associated cells, with each cell containing the addressing information sufficient to travel a path along the network interconnecting the sender and one or more recipients of the message. Packet switched networks are well suited to handling interactive traffic, and generally exhibit reduced delays and improved throughput in comparison networks incorporating circuit-switching. In contrast with circuit-switching which statically reserves the required bandwidth in advance, packet switching acquires and releases bandwidth as needed, so that bandwidth unused by one user may be used by another rather than being wasted.
ATM has been identified as a key technology for supporting voice, data, and multimedia services. For example, an ATM network is the underlying technology for a new wide area service called B-ISDN (Broadband Integrated Services Digital Network) which offers video on demand, live television from a variety of sources, full motion multimedia electronic mail, CD-quality music, LAN interconnection, high speed data transport, and other services.
Since the ATM network is connection-oriented, making a call requires first sending a message to set up the connection, after which subsequent cells follow the same path to the destination. After the call is complete, the connection is torn down. Furthermore, being connection-oriented, the order of cell delivery is guaranteed, but the delivery of ATM cells is not guaranteed. This order is particularly important for audio and video broadcast messages.
The main building blocks of an ATM network are ATM switches, which comprise the following three basic parts: the transport interfaces, the switch fabric, and the call processor. The transport interface recovers the information bits from the transmission waveforms. The switch fabric switches the ATM cells based upon the Virtual Path Identifier (VPI) and Virtual Circuit Identifier (VCI) indicators in the header of the ATM cell. The call processor routes, sets up, and tears down calls.
In prior art ATM networks, each ATM switch incorporates an associated call processor for establishing the connection. When the connection request arrives, the call processor examines the validity of the request, the availability of the required bandwidth, and the possibilities for routing within the network. The call processor then determines how the given ATM switches should be configured to establish a virtual path within the network necessary to make the connection. The call processor may need to communicate with a database in order to make this determination. New VPI and VCI indicators are configured for each connection, and the routing tables in the ATM switches are configured to establish the associated virtual paths and virtual circuits within the ATM network. Thereafter, ATM cells from a given source user terminal are coded with the appropriate VPI and VCI indicators in the associated headers so that the cells are routed along the proper virtual paths and virtual circuits within the ATM network. This cell-switching arrangement provides a number of associated advantages, including the flexibility to readily handle both constant (audio, video) and variable rate traffic (data), the facilitation of traditional multiplexing techniques using digital switching, and the accommodation of broadcasting from one sender to a plurality of receivers. Alternately, permanent virtual circuits may be established within the ATM network, by which the associated circuit connections remain in place for an extended period of time responsive to a prior agreement between the customer and the carrier, analogous to a leased telephone line.
When an ATM switch is located in a satellite, the associated switch hardware is essentially not upgradable, while the associated software may generally be upgraded to a limited extent. When routing a call, a satellite ATM switch exchanges signaling messages with the user terminal, other ATM switches, and databases. At any given time there could be, for example, a few hundred thousand connections or calls through the satellite, each call having associated states and signaling message exchanges, which require the associated satellite to have a complex call processor.
With the introduction of new telecommunication services and features, the call processor software and sometimes the hardware needs to be upgraded. One problem with prior art ATM switches that are remotely located, such as in a satellite, is that this may not be feasible. Satellite hardware is generally not upgradable, and satellite software may have only limited upgrade capabilities. While the software and sometimes the hardware of the call processor are routinely upgraded to support new telecommunication services and features, other elements of the ATM switch are generally relatively stable. Another problem with prior art ATM switches that are located in satellites and other remote locations and which incorporate a call processor, is the associated limitation on the weight and power consumption of the call processor, and the demands that the call processor has on associated support resources at the remote location. Yet another problem with prior art ATM switches is that when establishing a new connection, the process of generating new VPI and VCI indicators requires associated control messages that are a burden to the system, even for prior art systems where the call processor is physically separated from the associated switch fabric.
Accordingly, while it is generally desirable to both incorporate relatively simple electronics in the satellite and minimize the weight of any associated components, it is also desirable to efficiently utilize satellite bandwidth, and to provide new services and features as they emerge.
The instant invention overcomes the above-noted problems by providing an improved ATM network that incorporates a central call processor residing in a ground station in combination with remotely located ATM bridge nodes that incorporate the associated switch fabric. By physically separating the call processor from the switch fabric, and by physically locating the call processor at a conveniently located ground station, the associated remotely located electronics of the switch fabric can be simplified resulting in lower weight and power consumption, and in increase reliability and throughput. Moreover, by placing the call processor at a convenient location, the hardware or the software of the call processor may be readily upgraded as necessary to provide new services and features.
The remotely located ATM bridge nodes incorporate permanent ATM virtual paths that provide connections having flexible bandwidth resulting in a more efficient utilization of transmission resources of the remotely located ATM bridge node. When there is no user traffic on a particular permanent virtual path, only operations administration and maintenance (OAM) cells flow through the permanent virtual path as necessary, so that only a negligible amount of channel capacity is used for maintaining the permanent virtual path. The channel capacity that had been assigned to that particular permanent virtual path in a given transmission channel is then available to be used by other virtual paths in that channel for corresponding active virtual circuits therein. This results in providing bandwidth-on-demand resulting in a more efficient utilization of the satellite transmission capacity.
Signaling between the call processor and the remotely located ATM bridge nodes is not required for setting up, maintaining, or tearing down a new connection, unlike prior art ATM networks. Instead, signal message exchange takes place between the call processor, user terminals, other ATM switches, and data bases as required.
The permanent ATM virtual paths preclude the need for connection setup messages that would otherwise be required for configuring the ATM bridge switching fabric, thereby reducing the number of control messages to the bridge node and further increasing the bandwidth efficiency thereof. Furthermore, since the remotely located ATM bridge node incorporates permanent ATM virtual paths and therefore does not have to process control messages otherwise required to configure the switch for each connection, the processing throughput of the associated switch fabric is reduced, thereby increasing the efficiency of resource utilization in the remotely located ATM bridge node.
The remotely located ATM bridge nodes that relay ATM cells based upon an associated Virtual Path Identifier (VPI) are used to establish virtual path segments comprising one or more ATM bridge nodes within the network. The central call processor uses the virtual path segments to establish voice, data, or multimedia connections, but does not need to configure the ATM bridge to establish a new switched virtual connection since the associated ATM bridge node(s) incorporate permanent virtual paths that are generally reconfigured through the management interface, not through the signaling interface.
The above recited benefits are particularly pertinent to satellite based ATM bridge nodes, for which power and weight limitations are severe, for which reliability is important, for which physical access to make hardware changes is virtually impossible, and for which the extent of software upgrades is generally limited.
Accordingly, one object of the instant invention is to provide an improved ATM network that can be upgraded without having to access remotely located ATM bridge nodes. Another object of the instant invention is to provide an improved ATM network with improved throughput and reliability.
A further object of the instant invention is to provide an improved ATM network for which remotely located ATM bridge nodes can operate more efficiently and consume less power. A yet further object of the instant invention is to provide an improved ATM network with reduced overhead for establishing connections and with reduced processor throughput requirements at remotely located ATM bridge nodes.
In accordance with these objectives, the instant invention incorporates of one or more simplified ATM bridge nodes for which preestablished permanent virtual paths are defined that associate each signal input with one or more signal outputs in accordance with a Virtual Path Identifier (VPI) stored in an associated routing table. An accessibly located central call processor provides the particular VPI to the sending user terminal during the signaling process for establishing a connection with one or more receiving user terminals. Unused bandwidth from idle virtual paths or virtual circuits within a given transmission channel is made available to virtual paths and virtual circuits passing ATM cells within the transmission channel.
One advantage of the instant invention with respect to the prior art is that by incorporating a central call processor at a convenient location, the associated hardware and software can be readily repaired or upgraded, thereby increasing the adaptability and reliability of the communications system.
Another advantage of the instant invention is that by incorporating a central call processor at a convenient location, the weight and power requirements of the satellite ATM bridges are reduced, thereby providing improved throughput and reliability.
Yet another advantage of the instant invention is that by incorporating permanent virtual paths within the satellite ATM bridges whereby unused bandwidth from idle virtual paths or virtual circuits within a given transmission channel is made available to virtual paths and virtual circuits passing ATM cells within the transmission channel, the ATM bridges of the instant invention more efficiently utilize the transmission bandwidth capacity of the satellite.
These and other objects, features, and advantages of the instant invention will be more fully understood after reading the following detailed description of the preferred embodiment with reference to the accompanying drawings and viewed in accordance with the appended claims. While this description will illustrate the application of the instant invention in satellite communications network, it will be understood by one with ordinary skill in the art that the instant invention can also be applied to any ATM network, and particularly to ATM networks for which one or more ATM bridge nodes are placed at remote locations that are difficult to access.